This application claims priority under 35 U.S.C. Sec. 119 to No.10-376539 filed in Japan on Dec. 24, 1998, the entire content of which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a brake control system for a vehicle, with a brake-assist control function which assists a vehicle driver to operate a brake pedal, by increasing braking force automatically, when a brake pedal is depressed rapidly or deeply.
2. Description of the Related Arts
In the case where a brake pedal is rapidly depressed for an emergency braking purpose when driving a vehicle, for example, it will occasionally happen that sufficient braking force cannot be obtained, due to lack of depressing force, or hardly maintaining the depressing force. Even if the vehicle is provided with an ant-skid control system (ABS), the ant-skid control may not start due to lack of depressing force applied to the brake pedal, so that such a particular function may not be performed effectively. In view of those defects, it has been proposed to add a brake-assist control function, and some of them are already installed in vehicles on the market. The brake-assist control is the one for increasing the braking force automatically to assist a vehicle driver to operate a brake pedal, when the brake pedal is rapidly depressed, or the brake pedal is depressed deeply. For this purpose, a boosting function of a vacuum booster is controlled, in general. With the brake-assist control provided, therefore, the anti-skid control or the like can be performed effectively.
Also, it is known that the brake-assist control is performed by a pump for use in the anti-skid control system. In Japanese Patent Laid-open Publication No.8-230634, for example, a method and apparatus for controlling the anti-lock control system or a traction control system are proposed to save the power of the vacuum booster fully or partially. In that publication, it is assumed that the operation similar to the above brake-assist control may be performed, while the structure is not clear, due to its insufficient description. It is also assumed that when the brake-assist control is to be performed, an increasing gradient of the wheel cylinder pressure is controlled by turning on a pump motor, or controlling on/off of the motor, with an inlet valve placed in its open position, and with a changeover valve placed in its closed position. As a result, it may be possible to reduce a noise caused when driving the pump motor, comparing with that caused when driving the pump motor continuously. In that publication, however, nothing is described about the necessity for reducing the noise when the brake-assist control is being performed. Especially, when the brake pedal is deeply depressed to perform the brake-assist control, the pump is actuated frequently, so that the noise caused by actuating the pump will not be an issue to be neglected.
Accordingly, it is an object of the present invention to provide a brake control system which performs a brake-assist control by supplying the hydraulic braking pressure output from a hydraulic pressure pump, and which performs the brake-assist control quietly, by reducing a noise of a pressure pump actuated during the brake-assist control operation.
In accomplishing the above and other objects, a brake control system for a vehicle includes a wheel brake cylinder operatively mounted on each wheel of the vehicle for applying a braking force thereto, and a master cylinder for pressurizing brake fluid to supply a hydraulic pressure to the wheel brake cylinder in response to operation of a brake pedal. A cut-off valve is provided for opening or closing a main passage, which communicates the master cylinder with the wheel brake cylinder. A pump is provided for discharging the pressurized brake fluid to the wheel brake cylinder, with an outlet of the pump connected to a position between the cut-off valve and the wheel brake cylinder. An inlet valve is provided for opening or closing an auxiliary passage, which communicates an inlet of the pump with the master cylinder. And, a controller is provided for controlling the cut-off valve, inlet valve and pump. The controller is adapted to place the cut-off valve in a closed position thereof, place the inlet valve in an open position thereof, and actuate the pump to supply the pressurized brake fluid discharged therefrom into the wheel brake cylinder, so as to perform a brake-assist control. A detection device is provided for detecting an amount of operation of the brake pedal, so that the controller controls an amount of operation of the pump in response to variation of the amount of operation of the brake pedal detected by the detection device.
In the above described brake control system, preferably the detection device includes a pressure sensor for detecting a hydraulic pressure output from the master cylinder, and the controller is adapted to control the amount of operation of the pump, which is provided when it is determined on the basis of the output of the detection device that the master cylinder pressure is being decreased or held, to be smaller than the amount of operation of the pump, which is provided when it is determined on the basis of the output of the pressure sensor that the master cylinder pressure is being increased.
Preferably, the brake control system further includes an electric motor for actuating the pump, and the controller may be adapted to control a duty of a signal for driving the motor, which is provided when it is determined on the basis of the output of the pressure sensor that the master cylinder pressure is being decreased or held, to be smaller than the duty of the signal for driving the motor, which is provided when it is determined on the basis of the output of the pressure sensor that the master cylinder pressure is being increased.